Field
The disclosed concept pertains generally to systems for a network vault including a plurality of medium voltage feeders that form a network bus and, more particularly, to thermal control and monitoring systems for network vaults.
Background Information
Low voltage secondary power distribution networks consist of interlaced loops or grids supplied by two or more sources of power, in order that the loss of any one source will not result in an interruption of power. Such networks provide the highest possible level of reliability with conventional power distribution and are, normally, used to supply high-density load areas, such as a section of a city, a large building or an industrial site.
Each source supplying the network is typically a medium voltage feeder including a switch, a voltage reducing transformer and a network protector. As is well-known, a network protector is an apparatus used to control the flow of electrical power to a distribution network. The network protector includes a low voltage circuit breaker and a control relay which opens the circuit to the transformer upon detection of abnormal current flow. Specifically, the control relay typically senses the network voltages, the line currents and the phasing voltage, and executes algorithms to initiate circuit breaker tripping or re-closing actions. Trip determination is based on detecting reverse power flow, that is, power flow from the network to the primary feeder. Examples of network protector relays are disclosed in U.S. Pat. Nos. 3,947,728; 5,822,165; 5,844,781; and 6,504,693, which are incorporated by reference herein.
A network system is a redundant power delivery system including a plurality of primary feeders and associated network protectors. The transformer secondaries are electrically tied together through the network protector circuit breakers to a network bus, which increases the available fault current. However, as a result, workers can be exposed to arc flash hazards, which can cause equipment damage, serious bodily injury or even death if done improperly. A worker performing network protector manipulation is in physical proximity with the network protector. Therefore, the workers are typically required to wear approved personal protection equipment (PPE) to resist serious injury or death that could result if an electrical failure were to occur during racking/draw-out/draw-in operations.
Network protectors are typically used in the enclosed spaces of underground vaults. Since about 1922, network protectors have been installed in underground concrete vaults in major city centers. Since that time, such network protectors were designed as a switch that was bolted in place and required manual removal from a corresponding enclosure. The relatively extreme environment of a network protector demanded special components. As a result, standard power circuit breakers were not utilized. In about 1999, the assignee of the disclosed concept developed a network protector with a power circuit breaker suitable for that environment.
A known fire and ground fault protection system for a network vault includes a ground fault relay, a continuous fire detection (CFD) control board and indicators, and lockout relays for transformers and network protectors, including power supplies. An operator panel for this system includes indicator lights and trip/close pushbutton controls for the transformers and the network protectors. However, this system must be custom-wired when each transformer/network protector pair is added to the system. Hence, installation is both expensive and error prone. Also, no automated testing of every connection point is available from the operator panel. For example, known systems are implemented using discrete lights and switches for showing status, clearing faults, and operating switches and network protectors. However, safety interlocks to prevent system operation during testing are not incorporated.
There is room for improvement in thermal control and monitoring systems for network vaults.